1. Field of the Invention
The present invention relates to a heat resistant air hose to be used as a highly heat resistant air hose for transportation systems such as an automobile.
2. Description of the Art
As a material for forming a heat resistant air hose for use in automobiles or the like, acrylic rubber has conventionally been used. Tightened control on exhaust emissions and improvement of performance of supercharger (turbo charger) in high-powered engines in recent years have increased demands for extremely improved heat resistance for a heat resistant air hose. To meet such demands, silicone rubber having an excellent heat resistance is employed instead of the acrylic rubber. For example, there is proposed a hose consisting of an inner layer and an outer layer each formed of silicone rubber in which a reinforcing fiber layer is interposed between the inner layer and the outer layer. However, such a hose has a problem that the silicone rubber having insufficient oil-permeation resistance causes oil-bleeding phenomenon, that is, oil in a mist form coexisting in air flowing through the air hose penetrates the air hose from an interior surface thereof and reaches an exterior surface thereof.
To solve the above problem, there is proposed a heat resistant air hose having an inner layer formed of silicone rubber; and an innermost layer provided on an inner peripheral surface of the inner layer and formed of fluorinated rubber in, for example, Japanese Unexamined Patent Publication No. 2000-193152.
However, since the fluorinated rubber used for forming the innermost layer of the above hose is expensive, production costs of the hose are increased. Further, since the adhesion between the innermost layer of the fluorinated rubber and the inner layer formed of silicone rubber is not necessarily sufficient, interlaminar exfoliation may be caused when the hose is used as a heat resistant air hose, which may lead to various further problems. The fluorinated rubber is insufficient in low-temperature performance and also in resistance to an amine compound (amine-resistance), for example, an extreme-pressure additive, viscosity modifier or the like, added to engine oil. Further, since the above hose includes an outer layer formed of silicone rubber having a low dissipation factor (tan δ), the hose is considerably inferior in vibration transmission suppressibility, that is, the hose is inferior in suppressing transmission of vibration through the hose to conventional acrylic rubber hoses.
In view of the foregoing, it is an object of the present invention to provide a heat resistant air hose having excellent oil-bleeding resistance and vibration transmission suppressibility.